There is a wide variety of minerals in the US due to the large size of the country and its diverse geology. Economically speaking, the US is rich in many important resources including copper, lead, zinc, silver, gold, platinum group metals, iron, and building stone such as granite, marble, and basalt. Several regions have produced high quality gem minerals as well. A few locations in the US have extremely unique geology in which many minerals have been discovered.
The US has had an extensive history of mining which extends from prehistoric times to the present. Currently, the mining industry is not as active as it used to be but several large operations produce millions of tons of ore. The quest for ores of valuable metals and nonmetallic materials is what has driven the production of many specimens in the US including most of the specimens from the Southwestern states.
Many field collectors and amateur enthusiasts have also made discoveries by scouting outcrops and exposures for minerals. If a collector stumbles upon a find that is significant, they will often clean it and share the newly discovered occurrence at mineral club meetings, which have regional popularity in the US.
The United States is important because it has produced some of the finest examples of certain species of minerals and also has been the site of discovery for many. Below is a very brief list of some important localities that have produced fine, notable specimens or are mineralogically distinct.
The Sweet Home Mine in Alma, Colorado is arguably the single most famous mineral locality in the US. It has produced numerous highly valuable specimens of rhombic, neon pinkish red to cherry red rhodochrosite that can be gemmy and grow to an extremely large size. The former silver mine used to treat rhodochrosite as a gangue mineral. It was not realized to be valuable until mineral collectors and miners started saving it because of its beautiful color and crystallization.
The Minerva/Ozark-Mahoning Mine in Southern Illinois exploits one of the world’s largest reserves of fluorite and has produced extremely large and fine yellow and purple fluorites as well as some of the world’s best witherite, benstonite, strontianite, and baryte. Tens of thousands of specimens were removed from this now closed mine. While once inexpensive, they are now considered valuable and to have a high pedigree.
The town of Bisbee, Arizona has had a long history of producing huge amounts of copper. Its mines supplied the copper to build much of the early municipal copper plumbing in New York City. To mineral collectors, the name Bisbee is synonymous with amazingly fine malchite, azurite, and cuprite. Very large cabinet specimens of all three of these minerals have been collected from the mines in Bisbee, especially the Copper Queen Mine.
The Franklin Mining District in rural Northwestern New Jersey is the only location of its type- a primary zinc oxide deposit. The ore minerals are a highly fluorescent blend of willemite, zincite, and franklinite- the latter two being discovered and only occurring in appreciable quantity in Franklin. 70 minerals have been discovered in the district.
Benitoite is a rare mineral that forms gem crystals in high pressure metamorphic rocks exposed at a few small mines in San Benito County, California. Nowhere else in the world does this beautiful, lustrous blue mineral form crystals as large and gemmy as at this locality.
Few localities if any worldwide yield as many fine copper specimens as the Keweenaw peninsula in Michigan. This region is one of the few in the world that exploits veins of solid metallic running through basalt. None of the mines in the region are active, but many are still dug for specimens by intrepid collectors. Some of the specimens show extensive, large crystals. Some even are mixed with silver forming ìhalfbreedî nuggets.
The many pegmatites in Maine have been popular spots for mineral collectors in the urban areas of Boston and New York City to visit in attempts to collect their own high quality gem minerals. While the Maine pegmatites may not produce the most specimens of classic pegmatite minerals in the world, they produce specimens of considerable quality, uniqueness, and variety. Many different kinds of pegmatite minerals have been found in Maine including elbaite, morganite, heliodor, aquamarine, garnets, rose quartz, pollucite, amblygonite, topaz, and others.